<template>
	<el-color-picker
		v-model="theme"
		:predefine="['#409EFF', '#1890ff', '#304156','#212121','#11a983', '#13c2c2', '#6959CD', '#f5222d', ]"
		class="theme-picker"
		popper-class="theme-picker-dropdown"
	/>
</template>

<script>
    const version = require('element-ui/package.json').version; // element-ui version from node_modules
    const ORIGINAL_THEME = '#409EFF'; // default color

    export default {
        data() {
            return {
                chalk: '', // content of theme-chalk css
                theme: ''
            };
        },
        computed: {
            defaultTheme() {
                return this.$store.state.settings.theme;
            }
        },
        watch: {
            defaultTheme: {
                handler: function(val, oldVal) {
                    this.theme = val;
                },
                immediate: true
            },
            async theme(val) {
                await this.setTheme(val);
            }
        },
        created() {
            if (this.defaultTheme !== ORIGINAL_THEME) {
                this.setTheme(this.defaultTheme);
            }
        },

        methods: {
            async setTheme(val) {
                const oldVal = this.chalk ? this.theme : ORIGINAL_THEME;
                if (typeof val !== 'string') return;
                const themeCluster = this.getThemeCluster(val.replace('#', ''));
                const originalCluster = this.getThemeCluster(oldVal.replace('#', ''));

                const getHandler = (variable, id) => {
                    return () => {
                        const originalCluster = this.getThemeCluster(ORIGINAL_THEME.replace('#', ''));
                        const newStyle = this.updateStyle(this[variable], originalCluster, themeCluster);

                        let styleTag = document.getElementById(id);
                        if (!styleTag) {
                            styleTag = document.createElement('style');
                            styleTag.setAttribute('id', id);
                            document.head.appendChild(styleTag);
                        }
                        styleTag.innerText = newStyle;
                    };
                };

                if (!this.chalk) {
                    const url = `https://unpkg.com/element-ui@${version}/lib/theme-chalk/index.css`;
                    await this.getCSSString(url, 'chalk');
                }

                const chalkHandler = getHandler('chalk', 'chalk-style');

                chalkHandler();

                const styles = [].slice.call(document.querySelectorAll('style'))
                    .filter(style => {
                        const text = style.innerText;
                        return new RegExp(oldVal, 'i').test(text) && !/Chalk Variables/.test(text);
                    });
                styles.forEach(style => {
                    const { innerText } = style;
                    if (typeof innerText !== 'string') return;
                    style.innerText = this.updateStyle(innerText, originalCluster, themeCluster);
                });

                this.$emit('change', val);
            },

            updateStyle(style, oldCluster, newCluster) {
                let newStyle = style;
                oldCluster.forEach((color, index) => {
                    newStyle = newStyle.replace(new RegExp(color, 'ig'), newCluster[index]);
                });
                return newStyle;
            },

            getCSSString(url, variable) {
                return new Promise(resolve => {
                    const xhr = new XMLHttpRequest();
                    xhr.onreadystatechange = () => {
                        if (xhr.readyState === 4 && xhr.status === 200) {
                            this[variable] = xhr.responseText.replace(/@font-face{[^}]+}/, '');
                            resolve();
                        }
                    };
                    xhr.open('GET', url);
                    xhr.send();
                });
            },

            getThemeCluster(theme) {
                const tintColor = (color, tint) => {
                    let red = parseInt(color.slice(0, 2), 16);
                    let green = parseInt(color.slice(2, 4), 16);
                    let blue = parseInt(color.slice(4, 6), 16);

                    if (tint === 0) { // when primary color is in its rgb space
                        return [red, green, blue].join(',');
                    } else {
                        red += Math.round(tint * (255 - red));
                        green += Math.round(tint * (255 - green));
                        blue += Math.round(tint * (255 - blue));

                        red = red.toString(16);
                        green = green.toString(16);
                        blue = blue.toString(16);

                        return `#${red}${green}${blue}`;
                    }
                };

                const shadeColor = (color, shade) => {
                    let red = parseInt(color.slice(0, 2), 16);
                    let green = parseInt(color.slice(2, 4), 16);
                    let blue = parseInt(color.slice(4, 6), 16);

                    red = Math.round((1 - shade) * red);
                    green = Math.round((1 - shade) * green);
                    blue = Math.round((1 - shade) * blue);

                    red = red.toString(16);
                    green = green.toString(16);
                    blue = blue.toString(16);

                    return `#${red}${green}${blue}`;
                };

                const clusters = [theme];
                for (let i = 0; i <= 9; i++) {
                    clusters.push(tintColor(theme, Number((i / 10).toFixed(2))));
                }
                clusters.push(shadeColor(theme, 0.1));
                return clusters;
            }
        }
    };
</script>

<style>
.theme-message,
.theme-picker-dropdown {
  z-index: 99999 !important;
}

.theme-picker .el-color-picker__trigger {
  height: 26px !important;
  width: 26px !important;
  padding: 2px;
}

.theme-picker-dropdown .el-color-dropdown__link-btn {
  display: none;
}
</style>
